Outcomes from the EPECentre Workshop on Power Quality in Future Electrical Networks
June 2009
www.epecentre.ac.nz
DISCLAIMER
This document was prepared by the Electric Power Engineering Centre (EPECentre) at the University of
Canterbury in Christchurch, New Zealand. The content included in this document is based on a Power Quality
workshop held in April 2009. The EPECentre takes no responsibility for damages or other liability whatsoever from
the use of this document. This includes any consequential damages resulting from interpretation of material.
Electric Power Engineering Centre, University of Canterbury, New Zealand
Published by Electric Power Engineering Centre (EPECentre), University of Canterbury, New Zealand.
First edition, June 2009
Authors and Editors:
Assoc. Prof. Neville Watson, BE(Hons), PhD, CPEng, Int PE, SMIEEE, MIPENZ,
EPECentre, University of Canterbury, New Zealand
Prof. Vic Gosbell, BSc, BE(Hons), PhD, CPEng, MIEEE, FIEAust
Integral Energy Power Quality and Reliability Centre, University of Wollongong, Australia
Dr Stewart Hardie, BE(Hons), PhD, MIEEE
EPECentre, University of Canterbury, New Zealand
Acknowledgements:
Joseph Lawrence, EPECentre, University of Canterbury
Tas Scott, Orion NZ Ltd
Assoc. Prof. Sarath Perera, Integral Energy Power Quality and Reliability Centre, University of Wollongong,
Australia
Bill Heffernan, EPECentre, University of Canterbury
Peter Berry, Executive Director, EEA
Ken Smart, University of Canterbury
Dudley Smart, EPECentre, University of Canterbury
Sponsors and participants of the EPECentre Power Quality Conference and Workshop, 23-24 April 2009,
University of Canterbury, Christchurch, New Zealand.
Electric Power Engineering Centre
University of Canterbury
Private Bag 4800
Christchurch
New Zealand
T: +64 3 366 7001
E: info@epecentre.ac.nz
www.epecentre.ac.nz
© 2009 Electric Power Engineering Centre, University of Canterbury, Christchurch, New Zealand. All rights
reserved, no part of this publication may be reproduced or circulated without written permission from the Publisher.
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Power Quality in Future Electrical Networks
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Power Quality in Future Electrical Networks
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Power Quality in Future Electrical Networks
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Electric Power Engineering Centre
Outcomes from the EPECentre Workshop on
Power Quality in Future Electrical Networks
Contents
Preface............................................................................................................................................................6
1 Introduction to Power Quality....................................................................................................................7
1.1 What is Power Quality?......................................................................................................................7
1.2 Power Quality issues..........................................................................................................................7
1.2.1 Steady-state voltage..................................................................................................................10
1.2.2 Voltage dips (sags)...................................................................................................................10
1.2.3 Voltage imbalance....................................................................................................................10
1.2.4 Harmonics.................................................................................................................................10
1.2.5 Interharmonics..........................................................................................................................11
1.2.6 Transients..................................................................................................................................11
1.2.7 Light flicker due to voltage fluctuations...................................................................................11
1.3 Power Quality standards...................................................................................................................13
1.3.1 IEEE Standards ........................................................................................................................13
1.3.2 IEC 61000 series of Standards and Technical Reports.............................................................15
1.3.3 New Zealand standards.............................................................................................................18
1.4 Emission from existing equipment...................................................................................................19
1.4.1 Residential equipment..............................................................................................................19
1.4.2 Industrial equipment.................................................................................................................27
1.4.3 Distributed generation and inverters.........................................................................................29
1.4.4 Future equipment......................................................................................................................30
1.5 Immunity of equipment....................................................................................................................31
2 Summary of Power Quality Workshop....................................................................................................33
2.1 Question 1: Identification of significant Power Quality issues .......................................................33
2.2 Question 2: Data acquisition and use ..............................................................................................35
2.3 Question 3: Responsibility for Power Quality issues ......................................................................38
2.4 Wrap-up............................................................................................................................................40
2.5 Future challenges..............................................................................................................................41
3 Conclusions and future work...................................................................................................................42
4 Bibliography............................................................................................................................................43
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Preface
First of all, thank you to all those who attended the Power Quality in Future Electrical Networks
workshop. Your presence and participation made it the successful event that it was. It was a great time of
learning from each other, as well as making useful contacts.
Power Quality issues have been around for a long time. However, most of the time it does not feature in
people’s thinking until problems are experienced. Prevention is far better than curing problems after they
occur, hence the focus of this workshop. This document contains a summary of the workshop group
discussions, which we hope you will find informative. As a primer to the Power Quality area, a summary
of the international standards and the concepts underpinning them is included. Moreover, the measured
characteristics of existing and up-and-coming electrical equipment is given, so that you can be aware of
the likely impact equipment will have if widespread use is made of it. Finally, a comprehensive list of
books on Power Quality is given for further reading on this subject.
Assoc. Prof. Neville Watson
Associate, Electric Power Engineering Centre, University of Canterbury
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1 Introduction to Power Quality
1.1 What is Power Quality?
The geometry of synchronous generation results in a sinusoidal EMF being generated. This allows
transformation to higher voltages for efficient transmission of power. All equipment connected to the
electrical network is designed to operate with a sinusoidal voltage at rated value, as shown in Figure 1.
Power Quality, or more accurately Voltage Quality, is essential for electrical equipment to operate
correctly. Power Quality is the degree to which the supply voltage waveform conforms to the ideal
sinusoidal waveform (including magnitude and timing). Any deviation from this is a Power Quality issue.
Power Quality is a subset of ElectroMagnetic Compatibility (EMC), as depicted in Figure 2. The principal
phenomena causing ElectroMagnetic Compatibility issues are listed in Table 1. ElectroMagnetic
Compatibility refers to the ability of electrical and electronic equipment or systems to function
satisfactorily in the environment, without introducing intolerable disturbance to that environment. Thus it
implies that a limitation of emissions from equipment or systems is required, as well as a certain level of
immunity to interference which must be expected from other equipment and systems in that environment.
Emissions can be in the radiated or conducted form. Although power systems can be sources of radiated
emissions, radiated emissions from outside sources rarely affect the voltage waveform. Therefore in
Power Quality only conducted interference is of concern. Traditionally, Continuity of Supply (Reliability)
is considered as a separate class from Power Quality, however many would argue that the ultimate poor
Power Quality is having no voltage, hence Continuity of Supply is shown on the boundary in Figure 2.
1.2 Power Quality issues
Power Quality events can be classified into those that are discrete events (such as voltage dips/sags) and
those that are continuous (e.g. harmonics, steady-state voltage, flicker etc). Each of the more common
Power Quality problems will be introduced in the following sections.
Phase-to-neutral Voltage (Volts)
One suggested classification of voltage magnitude events is shown in Figure 3. Note that the boundaries
are somewhat arbitrary, for example the threshold between under-voltage and interruption is 1% of
nominal for IEC and 10% for IEEE. The classification according to IEEE standard 1159 is displayed in
Figure 4. Note that Voltage Dips and Voltage Sags are synonymous, the former term being used in
Europe and the latter in North America.
325.27
230 V
Figure 1: Ideal voltage waveform (also showing RMS value).
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ElectroMagneticCompatibility (EMC)
Frequency
Deviations
Continuity of Supply
Flicker due to Voltage (Reliability)
Surges/
fluctuations
Electric
Steady-state voltage
Swells
Fields
Impulse and
Switching
or more accurately
Transients
Power Quality
Voltage Quality
Harmonics
Sub-Harmonics
Inter-Harmonics
Unbalanced
3-phase
Voltages
Magnetic Fields
Waveshape
Faults
RF Radiation
High
Frequency
Noise
Figure 2: Power Quality as a subset of ElectroMagnetic Compatibility (EMC).
Table 1: Principal phenomena causing electromagnetic disturbances.
Conducted low-frequency phenomena
• Harmonics, Inter-harmonics
• Signalling voltages
• Voltage fluctuations
• Steady state voltage
• Voltage swells
• Voltage dips and interruptions
• Voltage unbalance
• Power frequency variations
• Induced low frequency voltages
• DC in AC networks
Radiated low-frequency phenomena
• Magnetic fields
• Electric fields
Conducted high-frequency phenomena
• Induced CW (continuous wave) voltages or currents
• Unidirectional transients
• Oscillatory transients
Radiated high-frequency phenomena
• Magnetic fields
• Electric fields
• Electromagnetic fields
• Continuous waves
• Transients
Electrostatic discharge phenomena (ESD)
Nuclear electromagnetic pulse (NEMP)
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Transient
120%
Very short
over-voltage
Short
over-voltage
Long
over-voltage
Very long
over-voltage
110%
100%
Normal operating Voltage range
Notch/transient
90%
1 to
10%
Very short
under-voltage
Short
under-voltage
Long
under-voltage
Very long
under-voltage
Very short
interruption
Short interruption
Long interruption
Very long interruption
0.5
cycle
1 to 3
cycles
1 to 3
hours
1 to 3
min.
Event Duration
120%
Transient
Figure 3: Suggested definition of voltage magnitude events. (Source: M. Bollen.)
Swell
Over-voltage
110%
100%
Normal operating Voltage range
Notch/transient
90%
Voltage Dip/Sag
Under-voltage
10%
Momentary
0.5
cycle
Temporary
3s
1
min.
Event Duration
Sustained Interruption
1-3 hours
Figure 4: Definition of voltage magnitude events according to IEEE Std. 1159 (1995).
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1.2.1 Steady­state voltage
Long term over-voltage or under-voltage is a major problem in many electrical networks around the
world. In New Zealand, the supply voltage is required to be 230 ±6%.
1.2.2 Voltage dips (sags)
A voltage dip is typically caused by a fault on the system or a large motor starting. The large current
flowing through the system impedance causes a depressed voltage until the fault is cleared or the motor
gets up to speed. If the retained voltage is very low (<10% IEEE or 1% IEC), it is classed as an
interruption instead of a voltage dip.
1.2.3 Voltage imbalance
There are a number of causes for the phase voltages to be imbalanced. Due to the geometry of overhead
transmission lines, the electrical parameters are different for the different phases unless transpositions are
used. Even with transpositions, unequal loading can create unbalanced voltages.
1.2.4 Harmonics
Any periodic waveform, such as the waveform in Figure 5, can be considered to be made up of a
fundamental with harmonic components. Hence a voltage or current waveform f(t) can be expressed as:
f t =
a0 ∞
∑ [ a cos n t b n sin n t ]
2 n=1 n
where an and bn are the Fourier coefficients. The magnitude and phase angle of the nth harmonic is given
by:
c n = an b n
−1
=tan
2
 
bn
an
2
1.5
1
Voltage (p.u.)
2
0.5
0
-0.5
-1
-1.5
-2
0
50
100
150
200
Time (degrees)
250
300
350
Figure 5: Example of harmonic distortion.
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There are numerous Power Quality indices derived from the harmonic components of a waveform, but the
most widely used is the Total Harmonic Distortion (THD), i.e. :
THD V =

∑
n
n
∑ V 2h
h= 2
THDI =
V1
I 2h
h=2
I1
The THD does not represent the ability to distort as it is a normalised index (normalised by fundamental
level), hence Total Demand Distortion (TDD) has been proposed as an alternative, i.e. :
TDDI =

50
∑ I 2h
h=2
I rated
For calculating the interference on telecommunication systems caused by harmonics and interharmonics,
two weighting systems are used, i.e.:
1. Psophometric weighting system proposed by the International Consultation Commission on
Telephone and Telegraph Systems (CCITT), used in Europe.
2. C-message weighting system proposed jointly by Bell Telephone System (BTS) and Edison
Electric Institute (EEI), used in the United States and Canada.
1.2.5 Interharmonics
With the introduction of Integral cycle controlled load and cyclo-converters, the waveform is not periodic
over the period of the fundamental and hence inter-harmonics and sub-harmonics are present. This is
demonstrated in Figure 6. Interharmonics can be also induced by some types of control signals.
1.2.6 Transients
Transient phenomena is also classified into impulsive transients (e.g. due to lightning) or oscillatory
transient (e.g. capacitor bank switching). Two examples are shown in Figures 7 and 8.
1.2.7 Light flicker due to voltage fluctuations
Voltage fluctuation that causes the fluctuations in the magnitude of the voltage envelope to have a
frequency component in the visual perception range (< 35 Hz), as shown in Figure 9, will cause light bulb
flicker. Voltage fluctuations due to amplitude modulation can be mathematically described by:
v t = 2 V  1mt   cost 
Consider for example the fundamental modulated by a purely sinusoidal voltage fluctuation i.e.:
mt =M cosm m 
The voltage waveform can then be seen to be made of three sine waves, a carrier and two sidebands:
v t = 2 V 1M cos m m  cost 
=  2 V  cost M cosm m cost  
=  2 V cos t 
1
1
 2 VM cos  m tm  2  2VM cos  − mt m 
2
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Figure 6: Cyclo-converter waveform which contains inter- and sub-harmonics.
Impulsive
Oscillatory
Figure 7: Voltage transients as defined in IEEE 1159.
Figure 8: A recorded voltage transient.
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Figure 9: Sinusoidal modulation of the voltage waveform.
1.3 Power Quality standards
The development of standards and guidelines is centred around the following:
1. Description and characterisation of the phenomena.
2. Major sources of power quality problems.
3. Impact on other equipment and on the power system.
4. Mathematical description of the phenomena using indices or statistical analysis to provide a
quantitative assessment of its significance.
5. Measurement techniques and guidelines.
6. Emission limits for different types and classes of equipment.
7. Immunity or tolerance level of different types of equipment.
8. Testing methods and procedures for compliance with the limits.
9. Mitigation guidelines.
1.3.1 IEEE Standards The United States (ANSI and IEEE) do not have such a comprehensive and complete set of Power
Quality standards as the IEC. IEEE 1159 (1995), as shown in Table 2, contains recommended practice on
monitoring electric power quality and categories of power system electromagnetic phenomena. The IEEE
Standard 519 is more specialised and is the IEEE recommended practice and requirement for harmonic
control in electric power systems, as shown in Tables 3 and 4.
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Table 2: Overview of IEEE Standard 1159.
Description
Transient
Impulsive
Nanoseconds
Microseconds
Milliseconds
Oscillatory
Low frequency
Medium frequency
High frequency
Short duration variation
Instantaneous
Sag
Swell
Momentary
Interruption
Sag
Swell
Temporary
Interruption
Sag
Swell
Long duration variations
Interruption, sustained
Under-voltage
Over-voltage
Voltage imbalance
Waveform distortion
DC offset
Harmonics
Interharmonics
Notching
Noise
Voltage fluctuations
Frequency variations
Spectral Content
Typical Duration
5 ns rise
1 µs rise
0.1 ms rise
< 50 ns
50 ns – 1 ms
>1 ms
<5 kHz
5-200 kHz
0.5-5 MHz
0.3 to 30 cycles
20 µs
5 µs
Magnitude
0.5 cycle to 3 s
0.5 cycle to 3 s
30 cycle to 3 s
30 cycle to 3 s
30 cycle to 3 s
3 s to 1 min
3 s to 1 min
3 s to 1 min
1-100th Order
1-6 kHz
Broad-band
<25 Hz
1.1 to 1.2 pu
> 1 min.
> 1 min.
> 1 min.
Steady-state
0.1 to 0.9 pu
0.8 to 0.9 pu
1.1 to 1.2 pu
Steady-state
Steady-state
Steady-state
Steady-state
Steady-state
Intermittent
<10 s
0 to 0.1 %
0 to 20%
0 to 2%
0 to 1%
Table 3: IEEE Standard 519 recommended harmonic voltage limits.
Maximum for individual harmonic
Total Harmonic Distortion
2.3-68.9 kV
3.0%
5.0%
69-138 kV
1.5%
2.5%
>138 kV
1.0%
1.5%
Table 4: IEEE Standard 519 current distortion limits for general distribution systems
in the range 120 V to 69 kV.
Maximum harmonic current distortion in %
Harmonic Order (odd harmonics)
Total Harmonic
Distortion
ISC / IL
<11
11 to 16
17 to 22
23 to 34
>35
<20
4.0
2.0
1.5
0.6
0.3
5.0
20 to 50
7.0
3.5
2.5
1.0
0.5
8.0
50 to 100
10.0
4.5
4.0
1.5
0.7
12.0
100 to 1000
12.0
5.5
5.0
2.0
1.0
15.0
>1000
15.0
7.0
6.0
2.5
1.4
20.0
ISC refers to the maximum short-circuit current at the PCC.
IL refers to the maximum demand load current (fundamental frequency component) at the PCC.
Even harmonics are limited to 25% of the odd harmonic limits above.
All generation power equipment is limited to these values of current distortion, regardless of actual short
circuit ratio.
For PCC from 69 kV to 138 kV, the limits are 50% of the limits above.
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1.3.2 IEC 61000 series of Standards and Technical Reports
ElectroMagnetic Compatibility (EMC) is the ability of equipment or system to function in its
electromagnetic environment without introducing intolerable disturbances to anything in that environment
(IEC 61000-1-1). The compatibility level is the specified disturbance level at which an acceptably high
probability of electromagnetic compatibility should exist. Each utility is to decide what emission margin
is appropriate for their system, based on the characteristics of their system and set a planning level which
is lower to give an emission margin. Likewise an appropriate immunity margin is needed to give an
immunity level which is larger than the compatibility level, for equipment manufacturers to design their
equipment to meet. This is illustrated in Figure 10 where the compatibility level is set to give a high
probability of electromagnetic compatibility. The rectangles show a range of possible planning levels and
immunity testing levels that may be chosen. These are at the discretion of the utilities and
regulatory/standard setting bodies. Compatibility levels are often set as a level to be achieved at least a
certain percentage of time, as demonstrated in Figures 11 and 12.
The IEC 61000 series of standards and technical reports are very comprehensive and the major
subdivisions are:
•
General (IEC 61000-1-x): The general section introduces and provides fundamental principles on
EMC issues and describes the various definitions and terminologies used in the standards.
•
Environment (IEC 61000-2-x): This part describes and classifies the characteristics of the
environment or surrounding where equipment will be used. It also provides guidelines on
compatibility levels for various disturbances.
◦ Harmonic compatibility levels of residential low voltage (LV) systems (IEC 61000-2-2)
◦ Industrial plants (IEC 61000-24)
◦ Residential medium voltage (MV) systems (IEC 61000-2-12).
•
Limits (IEC 61000-3-x): This section defines the maximum levels of disturbances caused by
equipment or appliances that can be tolerated within the power system. It also defines the
immunity limits for equipment sensitive to EMC disturbances.
◦ Harmonic current emission limits for equipment connected at LV with input current ≤16 A per
phase (IEC 61000-3-2).
◦ Flicker (IEC 61000-3-3): Limitation of voltage change equipment connected at LV with low
(< 16 A per phase) current.
◦ Harmonic current emission limits for equipment connected at LV with high (> 16 A per phase)
current (IEC 61000-3-4)
◦ Assessment of emission limits for distorting loads in MV and HV power systems (IEC 610003-6).
◦ Assessment of emission limits for voltage fluctuations in MV and HV power systems (IEC
61000-3-7).
◦ Assessment of emission limits for voltage fluctuations and flicker in LV power systems –
Equipment rated current < 75 A and subject to conditional connection (IEC 61000-3-11).
◦ Harmonic current emission limits for equipment connected at LV with input current >16A and
≤75 A per phase (IEC 61000-3-12)
•
Testing and Measurement Techniques (IEC 61000-4-x): These provide guidelines on the design of
equipment for measuring and monitoring Power Quality disturbances. They also outline the
equipment testing procedures to ensure compliance with other parts of the standards.
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Figure 10: Relationships between attributes of ElectroMagnetic Compatibility.
Disturbance Level
Percentage Time = 100*(t1+t2)/tTotal
x
t1
t2
Time
tTotal
Figure 11: Example of calculation of disturbance level time percentage.
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Figure 12: Two case studies that demonstrate percentage compatibility. Case 1 meets the
standard at least 95% of the time, while Case 2 meets the standard only 75% of the time. This
is irrespective of Case 2 levels often being much lower than Case 1 levels for much of the time.
◦ Harmonic and interharmonic measurements and instrumentation (IEC 61000-4-7)
◦ Dips and interruptions (61000-4-11)
◦ Interharmonics (61000-4-13)
◦ Testing and measurement techniques: Flickermeter – Functional and design specifications
(IEC 61000-4-15)
◦ Power Quality measurement methods (IEC 61000-4-30)
•
Installation and Mitigation Guidelines (IEC 61000-5-x): This section provides guidelines on the
installation techniques to minimise emission as well as to strengthen immunity against EMC
disturbances. It also describes the use of various devices for solving Power Quality problems.
•
Generic Standards (IEC 61000-6-x): These include the standards specific to certain category of
equipment or for certain environments. They contain both emission limits and immunity levels
standards.
IEC 61000-3-2 introduces Power Quality limits for four classes of equipment:
•
Class A: Balanced three-phase equipment and all other equipment, except those listed in other
classes.
•
Class B: Portable tools.
•
Class C: Lighting equipment, including dimming devices.
•
Class D: Equipment with a "special wave shape" and an input power of 75 to 600 W.
It is not widely appreciated that some of these publications are International Standards while others are
Technical Reports and hence do not have the same standing.
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1.3.3 New Zealand standards
New Zealand was one of the first countries to pass regulations in 1981 to limit the harmonic levels in the
electrical network (Limitation of Harmonic Levels Notice 1981, issued by the Office of the Chief
Electrical Inspector, Ministry of Commerce). This was due to the early installation of large rectification
equipment in the form of a HVDC link between the North and South Islands and aluminium smelter at
Tiwai point. This Limitation of Harmonics Notice 1981 now forms the basis of NZ Electrical Code of
Practice 36, which is cited in the Electricity Regulations 1997, making it a mandatory requirement. This
covers only allowable harmonic voltages and also indices covering telephone interference (EDV & EDI).
The code is split into requirements for when the Point of Common Coupling has a nominal voltage of less
than 66 kV, or 66 kV and above. All these limits are absolute, not statistical, however there is an
exception for control signals (i.e. ripple control).
Nominal voltage less than 66 kV
1. The phase-to-neutral harmonic voltage at any Point of Common Coupling with a nominal voltage
of less than 66 kV shall not exceed 4% for any odd numbered harmonic order, or 2% for any even
numbered harmonic order.
2. The Total Harmonic Voltage Distortion (THDV) at any Point of Common Coupling with a
nominal voltage of less than 66 kV shall not exceed 5%.
Nominal voltage of 66 kV or above
If the nominal voltage is above 66kV, the limits in Table 5 apply.
The equivalent disturbing voltage (EDV) shall not exceed 1% on any phase.
∑
50
EDV =6.25x10−5
nP n V n  2
n=2
where Pn is the weighting given to each frequency (from Psophometric weighting table).
Section 3 of this code of practice does give harmonic current limits, but only for 66kV, 110kV and
220kV.
New Zealand also has joint AS/NZS standards and these are clones of the IEC standard of the same
number. These at present are volunteering standards and some requirements (i.e. harmonic levels,
frequency deviation) conflict with the existing regulations.
Table 5: Harmonic voltage limits for nominal voltages of 66 kV or above.
Harmonic order
3
5
7
9
11
13
15
17 to 21
23 to 29
Harmonic voltage levels
(percentage phase-to-neutral values)
2.3
1.4
1.0
0.8
0.7
0.6
0.5
0.4
0.3
2
4
6
8 to 10
12 to 50
1.2
0.6
0.4
0.3
0.2
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1.4 Emission from existing equipment
The rectification process by which AC is converted to DC is a common source of harmonics. This process
is widely used in household appliances such as TVs, stereos, PC’s, microwave ovens, compact
fluorescent lamps, fluorescent lamps with electronic ballasts, LED lighting, and all types chargers (for
cell phones, cameras etc). The level of harmonic distortion is very much a function of the design of the
rectifier. The problem is that market forces put pressure on to cut costs, which results in a poorer rectifier.
1.4.1 Residential equipment
1.4.1.1 Compact fluorescent lamps (CFLs)
Block 1
Filtering and Protection
Block 2
Rectifier
Block 3
DC Filter
Block 4
Inverter and tube
PTC
Fuse
DIAC
Figure 13: Block diagram of a CFL
Power-Factor
Control Drive
Active filtering
No filtering
Passive filtering
Improved Valley-Fill
Figure 14: Various CFL filtering options presently in use.
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400
Basic, no filtering
600
Active Power-Factor
Control
300
400
200
Current (mA)
Current (mA)
200
0
-200
0
-100
-200
-400
-300
-600
0
0.005
0.01
Time (s)
0.015
0.02
-400
0
Basic, with filtering
600
0.005
600
400
400
200
200
Current (mA)
Current (mA)
100
0
-200
-400
0.01
Time (s)
0.015
0.02
Valley-fill or Equivalent
0
-200
-400
-600
-600
0
0.005
0.01
Time (s)
0.015
0.02
0
0.005
0.01
Time (s)
0.015
0.02
Figure 15: Current waveforms resulting from use of different CFL filtering options shown in Figure 14.
90
250
200
70
60
Current (mA)
RMS Current (mA)
Active Power-Factor
Control
Basic, no filtering
80
50
40
150
100
30
20
50
10
0
0
5
10
15
20
Harmonic Oder
25
0
0
30
90
Basic, with filtering
80
70
70
60
60
RMS Current (mA)
RMS Current (mA)
10
15
20
Harmonic order
25
30
35
90
80
50
40
30
40
30
20
10
10
5
10
15
20
Harmonic Oder
25
30
Valley-fill or Equivalent
50
20
0
0
5
0
0
5
10
15
20
Harmonic Oder
25
30
Figure 16: Current harmonics resulting from use of different CFL filtering options shown in Figure 14.
Outcomes from the EPECentre Workshop on
Power Quality in Future Electrical Networks
20
1.4.1.2 Personal computers
The current THD for a PC is typically between 70% to 120%. Below is a measurement on a PC with a
waveform with a THDI of 119%.
Current
10
5
Amps
0
-5
.
2.5
5.
7.5
-10
10.01 12.51 15.01 17.51
mSec
Current
2.0
1.5
Amps
1.0
0.5
0.0
DC
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Harmonic
Figure 17: Example current waveform and harmonics of a personal computer.
Figure 18: Example current waveform and harmonics of personal computer components.
Outcomes from the EPECentre Workshop on
Power Quality in Future Electrical Networks
21
Figure 19: Example current harmonics of personal computer components.
1.4.1.3 Microwave ovens
Current
50
25
Amps
0
.
2.51
5.02
7.53
10.04
12.55
15.06
17.57
-25
-50
mSec
Current
15
10
Amps
5
0
DC
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Harmonic
Figure 20: Example current waveform and harmonics of a microwave oven.
Outcomes from the EPECentre Workshop on
Power Quality in Future Electrical Networks
22
1.4.1.4 Stereos
A current THD of 38.8% was measured and this is typical of stereos.
Current
500
250
Amps 1Ø
0
.
2.5
5.
7.5
10.01
12.51
15.01
17.51
-250
-500
mSec
Current
150
100
Amps rms 1Ø
50
0
DC
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Harmonic
Figure 21: Example current waveform and harmonics of a stereo.
1.4.1.5 Heat­pumps
Figure 22: Example current waveforms of six different models of residential heat-pump.
Outcomes from the EPECentre Workshop on
Power Quality in Future Electrical Networks
23
1.4.1.6 Battery chargers
Current
50
25
Amps 1Ø
0
.
2.5
5.
7.5
10.01
12.51
15.01
17.51
-25
-50
mSec
Current
20
15
Amps rms 1Ø
10
5
0
DC
1
2
3
4
5
6
8
7
9
10
12
11
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Harmonic
Figure 23: Example current waveform and harmonics of a battery charger.
1.4.1.7 Digital camera
Current
100
50
Amps 1Ø
0
.
2.5
5.
7.5
10.01
12.51
15.01
17.51
-50
-100
mSec
Current
10
8
Amps rms 1Ø
6
4
2
0
DC
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Harmonic
Figure 24: Example current waveform and harmonics of a digital camera.
Outcomes from the EPECentre Workshop on
Power Quality in Future Electrical Networks
24
1.4.1.8 Mobile phone charger
Current
50
25
Amps
0
-25
.
2.51
5.02
7.53
-50
10.04 12.55 15.06 17.57
mSec
Current
20
15
Amps
10
5
0
DC
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Harmonic
Figure 25: Example current waveform and harmonics of a mobile phone charger.
1.4.1.9 Cordless phone charger
Current
50
25
Amps 1Ø
0
.
2.5
5.
7.5
10.01
12.51
15.01
17.51
-25
-50
mSec
Current
15
10
Amps rms 1Ø
5
0
DC
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Harmonic
Figure 26: Example current waveform and harmonics of a cordless phone charger.
Outcomes from the EPECentre Workshop on
Power Quality in Future Electrical Networks
25
1.4.1.10 Electronic photo­frame
Current
500
250
Amps 1Ø
0
.
2.5
5.
7.5
10.01
12.51
15.01
17.51
-250
-500
mSec
Current
30
25
20
Amps rms 1Ø
15
10
5
0
DC
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Harmonic
Figure 27: Example current waveform and harmonics of an electronic photo-frame.
1.4.1.11 Television
Figure 28: Example current waveform and harmonics of a television and video tape player.
Outcomes from the EPECentre Workshop on
Power Quality in Future Electrical Networks
26
1.4.2 Industrial equipment
Another major source of harmonic distortion is equipment used in industry and on dairy farms,
particularly the use of Variable Speed Drives (VSD). On dairy farms, VSDs for driving irrigation pumps
are a major harmonic source in rural networks with the 5th harmonic current often approximately 30% of
the fundamental current.
1.4.2.1 Irrigation pumps
AC
3
3
DC
DC
IM
AC
Figure 29: Schematic of a Variable Speed Drive.
Current
500
250
Amps
0
.
2.5
5.
7.5
10.01
12.51
15.01
17.51
-250
-500
Time mS
Current
200
33.2%
150
Amps rms
8.5%
100
8.0%
3.7%
50
0
DC
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Harmonic number
Figure 30: Example current waveform and harmonics of a Variable Speed Drive.
Outcomes from the EPECentre Workshop on
Power Quality in Future Electrical Networks
27
1.4.2.2 DC Drive
Because of the simplicity and precise motion control capability of DC Drives, as shown in Figure 31, they
find applications in printing presses, gondolas, and traction applications.
3
3
1
5
M
4
6
2
Figure 31: Schematic of a DC Drive system.
1.4.2.3 Metallurgical applications
Many metallurgical processes have a large impact on Power Quality: arc furnaces (AC, DC and induction
furnaces) as well as electroplating and refining processes.
1.4.2.4 Manufacturing
In manufacturing, conversion from AC to DC is often used. For example, one case that arose was in
making a product out of plastics. To ensure accurate control of the constituent compounds, thyristor
controlled heating elements were used, as shown in Figure 32. The machine had five three-phase thyristor
bridges driving a purely resistive element and the 5th harmonic current was 40% of the fundamental. The
AC side harmonic currents are a function of the DC side ripple and the 5 th harmonic increases as the
ripple increases.
3
3
5
4
6
2
R
1
Figure 32: Schematic of a thyristor controlled heating element.
Outcomes from the EPECentre Workshop on
Power Quality in Future Electrical Networks
28
1.4.3 Distributed generation and inverters
Inverters are an essential component to allow the energy from renewable sources to feed into an AC
electrical network. Many papers have been written about the harmonics introduced by photovoltaic
systems and this would be of great concern if the use of photovoltaic systems became widespread. Some
wind energy systems rectify the generator output and use an inverter to feed the energy into the AC
system. The design of the inverter that interfaces the DC source of energy determines the impact the
distributed generation will have on Power Quality. Figure 33 shows measured waveforms and spectrum
of two commercial inverters. It is clear that these waveforms are rich in harmonics and can detrimentally
affect cables (due to extra I2R losses) and voltage waveform.
Inverters are often used to reclaim energy that might otherwise be lost. In some applications, a process
can be used to generate DC, and this energy can be fed back to the AC system. One example would be in
combined heat and power systems, such as Whispergen, and similar schemes. These systems use energy
sources such as natural gas to provide heat. Electricity is generated from the waste heat and is fed back
into the AC system via an inverter.
Another Power Quality issue with distributed generation (particularly wind) is its intermittent nature and
how it fluctuates. These give rise to frequency stability issues and voltage fluctuations which cause lights
to flicker.
(a)
(b)
Figure 33: Example current waveform and harmonics of two commercial inverters.
Outcomes from the EPECentre Workshop on
Power Quality in Future Electrical Networks
29
1.4.4 Future equipment
There are several major future trends that could considerably impact on the Power Quality of the
electrical network. One of these is the widespread use of electric vehicles, such as the 2009 sample in
Figure 34. Various prototypes are already in service and full scale production will be within one year.
Although the initial uptake of electric vehicles is expected to be low, when the cost reduces and peoples'
confidence increases, they may well gain wide acceptance, particularly if they are heavily promoted. The
charging circuit again requires rectification and the same issues regarding the design of the rectifier and
its performance in terms of Power Quality is an issue. The charging requires a higher current than
available from the domestic 10A outlet and hence at present an electrician is required to wire in an outlet
with greater capacity in order to charge these vehicles.
LED lighting has the promise of giving higher efficiencies. A prototype LED system, shown in Figure
35(a), gives 30% more light for the same electrical consumption. They are also very flexible, with the
ability to colour correct and automatically adjust for lighting levels. There are also advantages for
specialist applications such as in hydroponics. The main barrier is cost. Again they run on DC and hence
require rectification.
Hot-water cylinders that use a heat-pump rather than a resistive element, as shown in Figure 35(b), are
already a commercial reality with most manufacturers offering this alternative. The Power Quality issues
associated with heat-pumps also apply to this, and if widely adopted would mean conversion of a
significant amount of the resistive loading of the system to a non-linear load. This has implications for
harmonics, voltage dips and voltage stability of the system.
Figure 34: Mitsubishi Innovative Electric Vehicle.
Outcomes from the EPECentre Workshop on
Power Quality in Future Electrical Networks
30
(a)
(b)
Figure 35: (a) Prototype LED lighting system and (b) hot-water cylinder that uses a heat pump (Source:
Quantum Energy Technologies).
1.5 Immunity of equipment
Immunity of equipment is an important aspect and changing the design to improve immunity of a
sensitive device (termed device hardening) is often more practical that reducing the disturbance level.
Over the years a number of bodies have developed standards for equipment immunity. The most wellknown is probably the 'CBEMA curve' (Computer Business Equipment Manufacturer Association),
shown in Figure 36. It was used to evaluate the voltage quality of a power system with respect to voltage
interruptions, dips or under-voltages and swells or over-voltages. This curve was originally produced as a
guideline to help CBEMA members in the design of the power supply for their computer and electronic
equipment.
CBEMA has been renamed as ITIC (Information Technology Industry Council) and a new curve, known
as the ITIC curve (shown in Figure 37) has been developed to replace the CBEMA curve. The main
difference between them is that the ITIC version is piecewise, and hence easier to digitise than the
continuous CBEMA curve. The tolerance limits at different durations are very similar in both cases.
Other curves have been developed such as SEMI47 which is designed for the semiconductor industry
requirements.
Testing the immunity of equipment, particular computer equipment for voltage dips has been reported in
the literature. Also work on what is known as 'device hardening' has been performed. The development of
super (ultra) capacitors now allows a level of energy storage on the DC busbar that was previously
unobtainable, and at a low price. This can give substantial improvement in immunity of equipment
relatively cheaply.
Market forces however cause manufacturers to trim their costs to compete with their competitors and this
usually reduces, rather than enhances, the equipment immunity (as well as device emissions).
Outcomes from the EPECentre Workshop on
Power Quality in Future Electrical Networks
31
Percent of Nominal Voltage
(RMS of Peak Equivalent)
400
300
200
106
Voltage Tolerance
Envelope
100
80
87
30
0
0.001
0.01
0.1ms
0.1
1ms
0.5 1 c
8.33ms
10 c
0.1s
100 c
0.5s
1000 c
2s
Time in cycles & seconds
Figure 36: CBEMA curve.
Percent of Nominal Voltage
(RMS of Peak Equivalent)
500
400
300
Prohibited Region
200
140
120
100
80
110
Voltage Tolerance
Envelope
90
No Damage Region
40
0
0.001
1 us
0.01
1c
1 ms
3 ms
10 c
20 ms
100 c
0.5 s
10 s
Steady
State
Time in cycles & seconds
Figure 37: ITIC curve.
Outcomes from the EPECentre Workshop on
Power Quality in Future Electrical Networks
32
2 Summary of Power Quality Workshop
This section presents a summary of the individual workgroup responses to three sets of questions
presented to them during the workshop, and a end-of-day 'wrap-up'.
2.1 Question 1: Identification of significant Power Quality issues What are the most significant Power Quality issues YOU are facing NOW? Mark and describe
those issues that have the most negative economic impact, and issues that receive the most customer
complaints.
NEI = Negative economic impact, CC = customer complaints
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Harmonics – Non linear loads, irrigation drives, HVDC, trains, DC inverters, thermal failure,
amplification due to capacitor banks
Voltage Dips – Motor starting, network faults, loss of production
Steady State Voltages – Low voltage and high load stressing networks (NEI, CC), high voltage
Voltage Unbalance – High voltages (NEI)
Flicker – Industrial loads (NEI, CC), wind farms, single phase loads
RF – Insulator design/sensitivity of equipment
DC components in/by transformers
Oversizing of transformers – Safety, future proofing, harmonics
Transmission – Unbalance (one phase loads, lack of transposition with high loads, harmonics)
Distribution – Flicker (short term soln CFLs), voltage variation (CC), sags not so bad,
proliferation of VSD motors, protection relay response to harmonics, quantifying in $$ cost of
poor PQ
Regulation influences
Compliance with regulations
Lack of equipment standards
Lack of consumer understanding
For UTILITIES, what are the most likely significant Power Quality issues to be faced in the
FUTURE? Why? Provide details of Power Quality issues, also considering excessive emissions,
immunity, and present or future regulator requirements.
•
•
•
•
•
•
•
•
•
•
•
•
•
Harmonics – Increasing levels
More distorting loads – VSD, CFLs, TVs
Less equipment immunity – Stricter regulations
Standards – Different application thereof, are they correct, complex, developing and enforcing
new standards
Distributed generation – Wind farms voltage control
Create awareness in community (education)
Derated equipment (Transformers/cables)
Uncertainty – Political, environmental
Future loads – What are they?
D.G and despatch rules
Economy
Traditional network design vs future design
Non compliance enforcement
Outcomes from the EPECentre Workshop on
Power Quality in Future Electrical Networks
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•
•
Customer responsibility
Evolving standards
For each of the following CUSTOMERS (a) to (c), what are the most likely significant Power
Quality issues to be faced in the FUTURE? Why?
(a) Industrial/commercial
•
•
•
•
•
•
•
•
•
•
Voltage sags
Compliance/standards
Poor design and installation practices leads to production losses
Education/good advice for customers
Short interruptions
Harden PLC
Spending more on quality
Increased penetration of sensitive equipment and import of PQ
Upgrade requirements due to changing PQ levels (allocation)
Embedded generation issues
(b) Rural
•
•
•
•
•
•
•
•
•
•
•
Voltage sags
Customer expectation
Increased use of electronics etc in low fault level areas
Education/good advice for customers
Drive failure due to PF cap switching and voltage dips
No filtering required on pumps and drives
Designed to urban standard?
Insurance stance?
Expectation doesn’t match the supplier capabilities
Disturbances die to interaction of different loads
Differential PQ Standards
(c) Residential
•
•
•
•
•
•
•
•
•
Voltage sags
Infill housing and steady state voltages
Increased non linear load (heat pumps, air con)
Education/good advice for customers
More rubbish on the market – Need a star rating for PQ?
High Voltage causing appliance failures and short life
Shifting load profile (night time charging) – Use of ripple control?
Expectation doesn’t match the supplier capabilities
More sensitive equipment – Voltage control with DG penetration, uptake of the Greenie
effect
Outcomes from the EPECentre Workshop on
Power Quality in Future Electrical Networks
34
2.2 Question 2: Data acquisition and use At each of the following points of the network (a) to (g), how much data acquisition equipment
should be installed by a UTILITY in the next 10 years? What should it record? If only a percentage
of multiple sites of the same class should have equipment installed, indicate what that percentage
should be. Weight the acquisition equipment/records as compulsory, highly recommended, or
useful.
A = compulsory, B = highly recommended, C = useful
(a) Grid exit point
Workgroup
V
I
Y
Y
3
4
% sites
measured
100%
100% 20%
80%
100%
5
100%
1
2
Unbalance
Harm
Fluct
Sags
Transients
Y
Y
Steady
state value
A
A
B
A
B
A
B
A
A
A
C
A
A
Y
A
Y
A
Y
A
Y
A
Y
B
Y
A
Y
C
Y
Y
Y
A
A
A
A
A
A
Unbalance
Harm
Fluct
Sags
Transients
B
A
A
Y
B
A
A
Y
B
A
B
Y
A
A
A
Y
C
A
B
Y
Another
quantity
CB Status –
Time Stamp
(b) Town substation
Workgroup
V
I
1
2
3
4
% sites
measured
100%
10-20%
5-10%
30%
Y
Y
A
Y
Y
Y
A
Y
Steady
state value
A
A
A
Y
5
50%
Y
Y
A
A
C
B
A
C
V
I
Unbalance
Harm
Fluct
Sags
Transients
Y
Y
A
Y
Y
Y
Y
A
Y
Y
Steady
state value
A
A
A
Y
A
B
A
A
Y
A
B
A
A
Y
B
B
B
B-C
Y
A
A
A
B
Y
A
C
B
B
Y
B
V
I
Unbalance
Harm
Fluct
Sags
Transients
Y
Y
A
Y
Y
A
Steady
state value
A
A
A
A
A
A
A
A
A
B
B
A
A
A
A
B
B
B
Y
Y
Y
Y
Y
A
Y
A
Y
A
Y
A
Y
A
Y
A
Another
quantity
CB Status –
Time Stamp
(c) Rural substation
Workgroup
1
2
3
4
5
% sites
measured
100%
30-50%
5%
100%
20%
Another
quantity
(d) Industrial site
Workgroup
1
2
3
4
5
% sites
measured
0-10%
1%
50%+
critical
Roaming
5%
Outcomes from the EPECentre Workshop on
Power Quality in Future Electrical Networks
Another
quantity
35
(e) Residential transformer
Workgroup
1
2
3
4
5
% sites
measured
<5%
0.1%
≤ 1%
Roaming
10
V
I
Y
Y
A
Y
Y
Y
Y
B
Y
Y
Steady
state value
A
A
A
Y
A
Unbalance
Harm
Fluct
Sags
Transients
A
A
A
Y
A
A
A
A
Y
A
B
B
B
Y
A
A
A
A
Y
A
B
B
A
Y
A
Steady
state value
A
A
A
Y
A
Unbalance
Harm
Fluct
Sags
Transients
A
A
A
Y
A
A
A
A
Y
A
C
B
Y
A
C
A
A
Y
A
C
B
A
Y
A
Another
quantity
Vn
(f) End of LV feeder
Workgroup
1
2
3
4
5
% sites
measured
<5%
0.01%
≤ 0.5%
Roaming
10
V
I
Y
Y
A
Y
Y
Y
Y
B
Y
Y
Another
quantity
Vn
(g) Another location of your choice (if time is available)
Workgroup
1
2
3
4
5
% sites
measured
V
I
Steady
state
value
Unbalance
Harm
Fluct
Sags
Transients
Generator
Connection:
Wind Farms
Third party
Gen & Rural
End User
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
A
A
A
A
A
A
Another
quantity
Other comments
•
•
•
•
•
•
Innovative graphical presentations
Envelope graphs
Cost is assumed to be low for instruments main cost is in data retrieval and analysis
Line Companies don’t own meters, contractual arrangements for access to data
Customer metering (non disclosure offshore particularly) – Data access represents
“regulator risk”
PQ monitors are relatively cheap and memory/storage is cheap
A rapidly increasing amount of raw data is being collected from the power system, and much more
data will be created in the future. For each of the following scenarios (a) to (e), what PRACTICAL
techniques and processes should be used to CONVERT collected raw data into useful Power
Quality awareness/knowledge of the network? Eg. for trouble-shooting, limits, planning and
investment. Also consider practical presentation of analysed data eg. 10 min averages, cumulative,
bar-graphs.
(a) Steady state voltage variation
•
Graph monthly/quarterly/yearly
Outcomes from the EPECentre Workshop on
Power Quality in Future Electrical Networks
36
(b) Voltage unbalance
•
Graph monthly/quarterly/yearly
(c) Harmonics
•
THD and 5th
(d) Voltage fluctuations (flicker)
•
Continuous PST < 1?
(e) Events (sags, transients)
•
Continuous
Other comments
•
•
•
•
•
•
Exceedances to be reported
Data used if network issues arise
Perhaps trend PQ issue – Project, other signals, circuit breaker status, time stamping
Standardisation of sampling/presenting
According to standards – 10 min to 1 week period
Lack of consistency
So that effective technical mitigation options may be studied, what are the barriers and good and
poor approaches to obtain Power Quality data (and system network information) from OTHER
UTILITIES or CUSTOMERS? Any specific experiences that have been witnessed that stand out?
Consider high-level political/commercial/personal relationships and agreements for data access or
acquisition. Consider low-level formatting of data, data standards and universal protocols.
•
•
•
•
•
•
•
•
•
•
•
Barrier to sharing – Commercial, closed mentality, utilities can lose access to data, revenue meters
owned by retailers
Different devices - Instruments hold data in different forms
Low level formatting can be an issue – 10 min cycles
Resourcing – Is there a cost benefit? Need utilities to take responsibility
No litigation data distribution and data sharing
International data format agreement
International standards agreement
Standardisation of sampling/presenting
Regulator issues
Planning – Working together with customers and regulators
Who pays?
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2.3 Question 3: Responsibility for Power Quality issues For each of the following equipment scenarios (a) to (e), what CRITERIA and WEIGHTING for
responsibility/costs should the UTILITY, EQUIPMENT MANUFACTURER/RETAILER and
CUSTOMER have for meeting future Power Quality conditions. Why?
(a) Rural customer's equipment that generate significant harmonic current injections.
Consider how harmonics should be allocated (device/site level, first come first served,
divided by expected number of connections, IEC declared customers)? Consider how
allocations should be enforced? What problems are there with present standards? Should
modifications be made to harmonic allocation levels in NZECP?
•
•
•
•
•
•
•
•
Equipment – Harmonic current limits (with inf. bus)
Utility – Harmonic voltage, perhaps connection charges?
Manufacturer, by agreement with utility
Use allocated share
Ratio of S/C capacity allocation
Rural/Urban – User pays
Utility = Standard, Equip/Mnf = Standard, Customer = Ongoing
Monitoring = IEC stds, utility. Costs = User.
(b) Residential heat pumps causing voltage sag and generating harmonic currents. Should
modified standards be introduced? What should they be?
•
•
•
•
•
•
•
•
Forced drop out and soft start
Manufacturer (not DOL)
Quality over price
Standard driven production
Quality driven by refined standards
Import guidelines – CF type tests?
Utility = Min standard of network required, Equip/Mnf = Standard
Monitoring = Stds, manufacturer. Costs = Manufacturer.
(c) Compact Fluorescent Lights generating harmonic currents. Should modified standards
be introduced? What should they be?
•
•
•
•
•
•
•
•
Enforce import standards for Ih
Manufacturer (not DOL)
Quality over price
Standard driven production
Quality driven by refined standards
Import guidelines – Tests?
Utility = Min standard of network required, Equip/Mnf = Standard
Monitoring = Stds, manufacturer. Costs = Manufacturer.
(d) Wind farms: system frequency stability, voltage sag and flicker. Consider large wind
farms and small DG wind farms. What about sub-20kW grid connected wind turbines,
especially in remote network sections?
•
•
IEC61400 – 21
Utility to require AS4777
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•
•
•
•
•
Large farms – Keep on line voltage regulation
Small farms – Safety
Responsibility – Grid operation, ensures compliance
Utility = Min level, Equip/Mnf = Network code, Customer = Ongoing
Monitoring = IEC stds, utility. Costs = Owner.
(e) Distributed Generation inverters at residential premises. Should modified standards be
introduced? What should they be?
•
•
•
•
•
•
A standard of some sort
DG – more on safety, same as d)
Utility = Min level, Equip/Mnf = Network code, Customer = Ongoing
Networks not designed for embedded DG at local level
Ongoing monitoring/policing/teeth
Monitoring = Manufacturer. Costs = Owner.
(f) Another scenario of your choice (if time is available).
•
Utility should be ultimate “policeman” to protect other and all users
What sort of information would be the most useful in a Power Quality guidelines booklet that helps
plan and mitigate present and future Power Quality issues? Eg. Case studies, bench marking,
calculation methods, other? Please update later if further suggestions arise in the future.
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Practical examples
Examples with typical solutions
Possible side effects
Review of standards/summary
Clarification and agreement of standards
Publicly available book
Increased awareness
Communication to end users
Equipment emission levels
Assessment criteria
Need to modify standards to suit NZ conditions
Education to local Electricians
Product standards heat pumps - realistic
Process flowcharts – Complaint, new installation, preventative
5 year review
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2.4 Wrap­up
This section contains the Power Quality workshop end-of-day 'wrap-up'. It consists of whiteboard notes
and floor comments about what were considered to be the important issues.
ECP36
•
•
Consensus to change it
Requirement to update standards, but do not want NZ only standards (too costly for manufacturers
to meet), therefore need international standards. Except if there is good grounds to vary eg. fault
levels reference impedance, current limits.
Emerging issues
•
•
•
•
•
DG – Political drive, subsidies, grid code to handle intermittent power injection, smart metering
Electric vehicles – Opportunities as well as threats, where is the generation, charging currents and
load management, smart metering could help, road tax issues
VSDs – also pumps in general, sag issues for big loads on long lines, general agreement on
harmonic issues.
Heat pumps – Load management, lobby standards committees for reasonable standards, the horse
has bolted??, hot water heat pumps, loss of load control through ripple control, use solar water
heating
Windfarms – Need grid code to handle intermittent power injection
Routine monitoring levels
•
•
GXPs (high need to monitor) – LV consumers (more statistical approach, need for utility smart
metering?)
PQ monitoring in smart metering, accuracy issues, who pays for more accurate meters?
Guidelines
•
•
Target audience – Customers, electricians (ENA guide, no techy talk), internal (HB264 starting
point, recommended practices, calc methods)
Application – Case studies, language, straight forward
Installation standards
•
•
•
•
Connections – Factories, farming, residential
Appliance standards
Extra categories in CEC star ratings, merge with efficiency in the future?
ANZS 61000 already available, are the numbers suitable for a compliance regime?
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2.5 Future challenges
What is the role of standards/regulations in Power Quality, or should a market approach be used?
If standards:
•
How is the permissible level set?
•
Should there be requirements on an installation or on each individual device?
•
Should the standard be absolute or 95% value?
•
Who has the responsibility for policing the Power Quality level?
•
How are interactions and resonances resolved?
•
Which customers should have priority on allocation?
33 kV
11 kV
Customer Customer Customer Customer
A
B
C
D
Customer Customer Customer Customer
E
F
G
H
Figure 38: Simple model of customers on a 11 kV feeder for Power Quality allocation purposes.
Outcomes from the EPECentre Workshop on
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3 Conclusions and future work
It is clear that Power Quality is an issue and will be more of an issue in the future with the uptake of new
technology. A few people prefer a market approach to Power Quality arguing that one limit does not
necessarily fit all. There was common consensus that standards and regulations are required to ensure the
addition of new equipment can be accommodated without any detrimental effects. This is because it is a
more practical way to deal with Power Quality issues, and there are pitfalls with a market approach. At an
industrial or commercial level it was felt that any standards should be on installations rather than on
individual items of equipment. This is because application to each item of equipment would restrict
availability or increase the equipment price, while a more cost effective solution may to deploy to
mitigation equipment in one place in the installation. On a domestic level, standards for individual items
of equipment were deemed more appropriate due to the impracticability of expecting each installation to
install mitigation equipment appropriate to the loading and the variability of the loading. Also the
incremental cost is very low to dramatically improve the device performance in low power domestic
appliances, hence minimum performance standards are required.
There are two sides to Power Quality: the emission levels and the immunity levels of equipment.
Coupling these is the network characteristics, as it controls for a given emission level, how high the
disturbance level generated is, and the next question is whether it is above or below the equipment’s
immunity level? New Zealand’s electrical network is a weak Island system due to our geographical
isolation from other electrical networks. Our system peak is approximately 6000 MW. This is very small
considering Europe, which is interconnected, United Kingdom, North America and our nearest neighbour,
Australia. This means that for a given emission level, it would be expected that a higher disturbance level
would result with a smaller system (ignoring the possibility of resonances). Much of the future work
revolves around investigating what a typical New Zealand electrical system can withstand in terms of
steady-state and transient disturbance. Normally the voltage quality is the key quantity and the measure of
the disturbance level, while current specification characterises the emission level. To allocate emission
limits to installations and equipment while ensuring the disturbance level does not exceed the planning
level requires knowledge of the system impedance.
The relevant IEC publication is IEC/TR 60725, entitled “Consideration of reference impedances and
public supply network impedances for use in determining disturbance characteristics of electrical
equipment having a rated current ≤ 75 A per phase”. Tables 6 and 7 show data from this technical report,
some of which is measured and the rest based on calculations.
Table 6: Single-phase service capacities <100 A per phase.
Country
Canada
USA
Korea
Japan
100-120 V
0.2+j0.06
0.09+j0.05
0.35+j0.13
200-400V
0.2+j0.08
0.1+j0.06
0.67+j0.37
0.42+j0.21
Table 7: Three-phase service.
Country
Canada (120/208V)
USA (277/480V)
Korea (230/400V)
Japan (200V)
Capacities<100A per Phase
0.07+j0.04
No data
0.33+j0.2
No data
Capacities>100A per Phase
0.39+j0.07
No data
0.26+j0.3
No data
Outcomes from the EPECentre Workshop on
Power Quality in Future Electrical Networks
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4 Bibliography
Arrillaga J., Chen S. and Watson N.R.
Power System Quality Assessment
John Wiley & Sons 2000
Arrillaga J. and Watson N.R.
Power System Harmonics 2nd Edition
John Wiley & Sons 2003
B. Kennedy
Power Quality Primer
McGraw-Hill 2000
R.S. Vedam & M.S. Sarma
Power Quality: VAR Compensation in Power Systems
CRC Press 2009
M.H.J. Bollen
Understanding Power Quality Problems
IEEE 2000
E.F. Fuchs & M.A.S. Masoum,
Power Quality in Power systems and Electrical Machines
Elsevier 2008
G.T. Heydt
Electric Power Quality
2nd Edition
Stars in a Circle Publications 1991
C. Sankaran
Power Quality
CRC Press 2002
F. C. De La Rosa
Harmonics and Power Systems
CRC Press 2006
R.C. Dugan, M.F. McGranaghan and H.W. Beaty
Electrical Power Systems Quality
McGraw-Hill 1996
Outcomes from the EPECentre Workshop on
Power Quality in Future Electrical Networks
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Antonio Moreno-Muñoz (Ed.)
Power quality : mitigation technologies in a distributed environment
Springer 2007
By A. Kusko and M. T. Thompson
Power quality in electrical systems
McGraw-Hill Professional, 2007
Angelo Baggini
Handbook of Power Quality
John Wiley & Sons Inc. 2008
G.J. Wakileh
Power Systems Harmonics: Fundamentals, Analysis and Filter Design (Hardcover)
Springer 2001
W. Mielczarski, G.J. Anders, M.F. Conlon, W.B. Lawrence, H. Khalsa and G. Michalik
Quality of Electricity Supply & Management of Network Losses
Puma Press, Melbourne, 1997
T.A. Short
Distribution Reliability and Power Quality
CRC Press 2006
A. Ghosh and G. Ledwich
Power Quality Enhancement using CUSTOM Power Devices
Kluwer Academic Publishers, 2002
Mohammed S. S. Al-Mandhari
Improving Voltage Dip Ride-through Using Super/Ultra Capacitors, 2008 Third Professional Year
Project, Electrical & Computer Engineering Department, University of Canterbury, 2008
Outcomes from the EPECentre Workshop on
Power Quality in Future Electrical Networks
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